This invention relates to flexible seals, of the kind comprising an envelope and a packing in the envelope. The invention has particular but not exclusive application to static seals for glass-lined vessels, for example pressure vessels.
A problem which arises in the sealing of pipes and vessels, is that the flange surfaces or other sealing surfaces are often less than perfectly flat.
This problem is particularly serious in the case of glass-lined vessels, which commonly have flange surfaces out of flatness both circumferentially and radially. Distortion of the flange surfaces occurs when the glass powder that has been sprayed onto the vessel surfaces is fused, the fusing temperature being in the region of 750.degree. C.
In a glass-lined vessel, apertures may need to be sealed over a range of sizes from 1 inch (25 millimeters) diameter to 7 feet (213 centimeters). The required seal thickness may vary from 1/16th of an inch to 1/2 inch (1.5 to 12.7 mm).
In the past, seals have commonly contained asbestos, and have been inefficient and have required considerable amounts of time for installation and replacement.
An object of the present invention is to provide a flexible seal, suitable for sealing glass-lined vessels and in other circumstances where sealing surfaces are not perfectly flat, which seal will not contain any asbestos or other harmful materials, and will provide high seal efficiency, reduced seal assembly time, and a substantial decrease in down-time of the equipment involved.
Our British Patent Application No. 9017173.7 filed 6th Aug. 1990 disclosure seals capable of achieving these objects, for thicker seals, typically 4.7 mm or more thick. The seal proposed in the aforesaid application comprises an envelope, and a packing within the envelope, the packing comprising a plurality of adjacent turns of strip material, arranged with the width direction of the strip extending generally perpendicular to the sealing faces of the seal, the strip material being resilient and having apertures extending through it, distributed along the strip length, whereby the strip is resilient in the direction of its width.
In a preferred embodiment, the strip material is stainless steel or other suitable metal and the envelope is PTFE.
A specific object of the present invention is to provide a seal capable of overcoming the shortcomings of conventional seals and achieving the above-mentioned objects, in a small seal thickness, typically 4 mm thick or less.